Method for improving heat efficiency using silane coatings and coated articles produced thereby

ABSTRACT

Oligomeric silane coating compositions containing, for example, methyltrimethoxysilane, are used to coat new or used heat exchange apparatus, such as HVAC systems, to greatly improve the heat transfer efficiency and prevent or inhibit corrosion. These oligomeric coating compositions are able to fill microvoids in the heat exchange surfaces, and penetrate into the microcavities at the interface of swaged or force fit surfaces, such as fins and tubes. The oligomeric silane coating compositions are highly active and will form bonds not only with the metal and metal oxides of the heat transfer surfaces, but will also displace gasses or liquids at the heat transfer contact surfaces and form chemical and/or hydrogen bonds with the oxides and chemical impurities. By so doing, a parallel heat transfer pathway is formed. The applied coatings may be as thin as only a few millionths of an inch and will fill microcavities to a depth of up to about 2000 nanometers. The coated heat transfer surfaces are non-adherent to deposition of soils and microorganisms and, therefore, are easier to maintain and are environmentally safe for use to heat/cool inhabited structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Provisional ApplicationsNos. 60/181,061, 60/185,354, 60/185,367, and 60/236,158, filed Feb. 8,2000, Feb. 28, 2000, Feb. 28, 2000, and Sep. 29, 2000, respectively.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to use of silane based coatingcompositions for coating heat exchange systems, such as HVAC systems,whereby heating efficiencies and corrosion protection are bothsubstantially improved. More particularly, the present invention isconcerned with improving performance and useful lifetime of heatexchange systems wherein the heat exchange surfaces are coated with avery thin coating of glass-like silane based coating composition whichpenetrate into very small spaces at the interface between and in theheat exchange surfaces to provide a parallel path for heat transfer andprevent corrosion, thereby greatly improving short- and long-termefficiency.

[0004] 2. Discussion of the Prior Art

[0005] Silane, silanol and siloxane compounds have been used for manyyears, as both solvent-based and aqueous-based, formulations, with orwithout modification with organic substituents, for such applications ascoupling agents for glass or other inorganic substrates to organiccompounds; non-permanent (limited life) water repellants for concreteand woven fabric materials; synthetic rubber like compounds foradhesives and sealers; adhesion modifiers for organic paints andinorganic coatings; and other property enhancing uses which takeadvantage of having the ability to form moderate to strong hydrogenbonds to organic and inorganic surfaces, more tenaciously than mostclasses of polymeric coatings.

[0006] U.S. Pat. Nos. 3,944,702, 3,976,497, 3,986,997 and 4,027,073describe coating compositions which are acid dispersions of colloidalsilica and hydroxylated silsequioxane in an alcohol-water medium.

[0007] U.S. Pat. No. 4,113,665 discloses chemically resistant ambientcurable coatings based on a binder of which the major portion isprepared by reacting, in an acidic solution, trialkoxysilanes (e.g.,methyltriethoxysilane) with aliphatic polyols, silicones or both. Bariumfillers, such as barium metaborate, may be added to provide resistanceto sulfur dioxide. Zinc oxide or metallic zinc may be included forfurther corrosion resistance. The compositions may be applied to, e.g.,steel petroleum tanks, by spraying, concrete, vitreous surfaces.

[0008] U.S. Pat. No. 4,413,086 describes water reducible coatingcompositions containing organosilane-polyol which is a reaction productbetween certain hydrophilic organic polycarbinols and organosiliconmaterial, e.g., organosilane, curing agent (e.g., aminoplast resin),organic solvent (optional), essentially unreacted polyol (optional),essentially unreacted hydrolyzed and condensed organosilane (optional),water (optional) and pigment (optional).

[0009] U.S. Pat. No. 4,648,904 describes an aqueous emulsion of (a)hydrolyzable silane, inclusive of methyltrimethoxysilane, (b) surfactant(e.g., Table I, col. 4) and (c) water. The coatings may be used forrendering masonry water repellant.

[0010] U.S. Pat. No. 5,275,645 is purported to provide an improvement tothe acid-catalyzed organosilane coating compositions of theabove-mentioned U.S. Pat. No. 4,113,665. According to this patent aprotective coating is obtained at ambient temperature from a coatingcomposition containing organosilanes having an Si—O bond, using an aminecatalyst and an organometallic catalyst.

[0011] U.S. Pat. No. 5,879,437 describes a coating compositioncontaining a tetraalkyl silicate or monomeric or oligomeric hydrolysisproduct thereof, present in a proportion of 40-90% by weight based onthe non-volatile content of the composition and a hydrous oxide sol(Type A or Type B), in an amount such that the oxide constitutes 10-60%by weight of the non-volatiles. According to the patentees, this coatingcomposition is suitable for the pretreatment of solid surfaces such asmetals generally, including steel, titanium, copper, zinc and,particularly aluminum, to improve adhesion properties of the pretreatedsurface to subsequently applied coatings, such as paint, varnish,lacquer; or of adhesive, either in the presence or absence of alubricant.

[0012] U.S. Pat. No. 5,882,543 describes methods and compositions fordehydrating, passivating and coating HVAC (heating, ventilating and airconditioning) systems. The compositions include an organometalloidand/or organometallic compound, which reacts with water in the system.The sealing function of these compositions is apparently obtained byintroducing the composition to the fluid enclosure and upon exiting froman opening, the composition (i.e., organometallic) reacts withatmospheric moisture to seal the opening.

[0013] U.S. Pat. No. 5,954,869 discloses an antimicrobial coating fromwater-stabilized organosilanes obtained by mixing an organosilane havingone or more hydrolyzable groups, with a polyol containing at least twohydroxyl groups. This patent includes a broad disclosure of potentialapplications and end uses, e.g., column 4, lines 35-53; columns 23-25.

[0014] U.S. Pat. No. 5,959,014 relates to organosilane coatingspurported to have extended shelf life. Organosilane of formulaR_(n)SiX_(4−n) (n=0-3; R=non-hydrolyzable group; X=hydrolyzable group)is reacted with a polyol containing at least three hydroxyl groups,wherein at least any two of the at least three hydroxyl groups areseparated by at least three intervening atoms.

[0015] U.S. Pat. No. 5,929,159, to J. Schutt and A. Gedeon, and commonlyassigned with the present application, describes an oligomeric coatingcomposition in the form of an aqueous composition comprising adispersion of divalent metal cations (especially, Ca, Mn, Cu and Zndivalent ions) in lower aliphatic alcohol-water solution of the partialcondensate of at least one silanol (at least about 70 wt. % of which wasmethyltrimethoxy silane), and acid, in amount to provide a pH in therange of from about 2.5 to about 6.2, the amount of the divalent metalcations being from about 1.2 to about 2.4 millimoles, per molarequivalent of the partial condensate, calculated as methyl silanesesquioxide. It is also described to provide a coating composition as atwo part formulation, the first part being an acidic aqueous dispersionof divalent metal cation, having a pH of from about 2.2 to about 2.8;and the second part a non-aqueous composition comprising at least onetrialkoxy silane; with at least one of the first and second partscomprising a volatile organic solvent. The corrosion resistant coatingsmay be provided as aqueous-alcoholic dispersions of the partialcondensate of monomethyl silanol (obtained by hydrolysis of monomethylalkoxysilane) alone or in admixture with minor amounts of other silanol,e.g., phenyltrimethoxysilanol, gamma-glycidyloxy silanol, and the like,wherein the reaction is catalyzed by divalent metal ions, e.g., Ca⁺²,typically from alkaline earth metal oxides. When these coating areapplied to, e.g., boat hulls, such as aluminum hulls, they are highlyeffective in preventing corrosion from salt water for extended periods.

[0016] Thus, this patent indicates that the patented coatingcompositions are suitable for application to various types ofsubstrates, but especially, marine surfaces, such as aluminum boathulls, to render the surface corrosion resistant in a salt waterenvironment. Other representative potential applications and substratesfor the patented silane based coating compositions mentioned in theSchutt and Gedeon patent include coatings for concrete/rock, wherein thecoating can penetrate the porous materials, due to its low viscosity andactive nature; metals/plastics, wherein the coating is preferablyapplied to very clean surfaces but will itself clean the pores in themetal or plastic and exhume the contamination which generally rises tothe surface of the coating.

[0017] The compositions of the Schutt, et al patent are oligomericcoatings using a variety of siloxane bond forming monomers as described.Subsequent modifications of the compositions of the U.S. Pat. No.5,929,159 patent have been developed by John Schutt and are described,for example, in copending provisional applications Serial Nos.60/185,367 and 60/185,354, both filed on Feb. 28, 2000, and Serial No.60/236,158, filed Sep. 25, 2000. Basically, these provisionalapplications disclose formulations for silane/siloxane/silanololigomeric compositions, both solvent (non-aqueous) and water (aqueous)based, which effectively bond to many different metallic andnon-metallic surfaces by means of siloxy (—Si—O—) bonds.

[0018] The compositions disclosed by the U.S. Pat. No. 5,929,159 patentand provisional applications can cure under ambient conditions and arecatalyzed using, for example, acid, alkali, and metal alkoxide,catalysts. They may contain organic additives forming hydrogen bonds ofgreater energy than those formed with water. Protection of metallicsurfaces occur because bonds of greater covalency are created which aremore robust than dipole or dispersion forces.

SUMMARY OF THE INVENTION

[0019] It has now been discovered that the coating compositions of U.S.Pat. No. 5,929,159, and subsequently developed formulations, asdescribed in the aforementioned three provisional applications, Ser. No.60/185,354, 60/185,367, and 60/236,158, the entire disclosures of whichare incorporated herein, in their entireties, by reference thereto, arevery highly effective in providing strongly adherent, corrosionresistant coatings for heat exchange systems, including, especially, airconditioning units and other HVAC systems, and the individual componentsthereof. Although not wishing to be bound by any particular theory ofoperation, it is believed that the effectiveness of these siloxy bondforming coating compositions arises, at least in part, from theoligomeric nature of these compositions. The low molecular weight of theoligomeric components and the low viscosity of the composition, enablesthem to penetrate the defect surface structure found in all surfaces,with the option of creating dendritic-like networks over a surface. Inparticular, scanning electron microphotographs show that compositions asdescribed herein penetrate defects having nanometer dimensions whileforming films on the order of millionths of an inch in depth.

[0020] These compositions may be applied not only to coat new heatexchange systems and component parts thereof, e.g., coils, condensersand the like, but also may be applied in situ to existing heat exchangesystems and component parts, even when the system or individual partsthereof are corroded.

[0021] Accordingly, the present invention provides a method forimproving heat exchange (thermal) efficiency of heat transfer surfacesand corrosion protection for heat transfer surfaces and heat transfersystems and component parts thereof by coating the heat transfersurfaces alone or the entire heat transfer system or component partsthereof, with a low viscosity, penetrating, reactive, curable,film-forming, silane-based, coating composition and curing thecomposition to thereby form an at least substantially continuousglass-like coating on the coated surface, the coating extending intovoids and defects which may be present in the surface, whereby athermally conductive corrosion protective layer is provided on the heattransfer surface, and any other coated surfaces.

[0022] In one embodiment, the present invention provides a method forimproving efficiency of heat transfer from a heat transfer mediumflowing in heat transfer contact with a heat transfer surface of athermally conductive component of a heat transfer system across the heattransfer surface.

[0023] In a particularly preferred embodiment of the invention, thecoating composition is applied to at least the heat exchange surfaces ofa fin and tube heat exchange system.

[0024] In the preferred embodiment of the invention, the coatingcomposition is an aqueous or non-aqueous oligomeric silane coatingcomposition formed by admixing (a) at least one silane of the formula(1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0025] where R¹ represents a lower alkyl group, a C₆-C₈ aryl or afunctional group including at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional groups;

[0026] (b) silane condensation catalyst, and

[0027] (c) lower alkanol solvent, and optionally, one or more of

[0028] (d) colloidal aluminum hydroxide;

[0029] (e) metal alcoholate of formula (2):

M(OR³)_(m)  (2)

[0030] where M is a metal of valence 2, 3 or 4, or mixture of two ormore such metals;

[0031] R represents a lower alkyl group; and,

[0032] m represents a number or 2, 3 or 4;

[0033] (f) a silica component selected from the group consisting ofalkali metal silicate, ethyl orthosilicate, ethyl polysilicate, andcolloidal silica dispersed in lower alkanol;

[0034] (g) color forming silanol condensation catalyst;

[0035] (h) epoxysilane; and,

[0036] (i) ultrafine titanium dioxide ultraviolet light absorber.

[0037] The coating composition is applied to at least a portion of aheat transfer surface and the applied coating composition is allowed tocure to form a highly corrosion resistant and strongly adherent coating.This coating is effective to fill micropores and crevices in the heattransfer surface to effectively increase the area available for heattransfer.

[0038] Similarly, the present invention provides a method for increasingthe contact area between first and second heat transfer surfaces inthermal contact with each other, thereby improving the heat transferefficiency across the thermally contacting heat transfer surfaces. Themethod according to this embodiment comprises applying to the thermallycontacting heat transfer surface of at least one of the first and secondheat transfer surfaces, a low viscosity, penetrating, curable, reactive,film-forming, coating composition and curing the composition to therebyform an at least substantially continuous glass-like coating on the heattransfer surface, the coating extending into voids and defects which maybe present in said heat transfer surface, whereby a thermally conductivecorrosion protective layer is provided on the heat transfer surface.

[0039] Here again, the preferred coating composition is an aqueous ornon-aqueous oligomeric silane coating composition formed by admixing (a)at least one silane of the formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0040] where R¹ represents a lower alkyl group, a C₆-C₈ aryl or afunctional group including at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional groups;

[0041] (b) silane condensation catalyst, and

[0042] (c) lower alkanol solvent, and optionally, one or more of

[0043] (d) colloidal aluminum hydroxide;

[0044] (e) metal alcoholate of formula (2):

M(OR³)_(m)  (2)

[0045] where M is a metal of valence 2, 3 or 4, or mixture of two ormore such metals;

[0046] R represents a lower alkyl group; and,

[0047] m represents a number or 2, 3 or 4;

[0048] (f) a silica component selected from the group consisting ofalkali metal silicate, ethyl orthosilicate, ethyl polysilicate, andcolloidal silica dispersed in lower alkanol;

[0049] (g) color forming silanol condensation catalyst;

[0050] (h) epoxysilane;

[0051] (i) ultrafine titanium dioxide ultraviolet light absorber;

[0052] (j) water; and

[0053] (k) co-solvent.

[0054] In a particularly preferred embodiment, the efficiency of heatexchange apparatus of the type wherein a metal-to-metal contact ispresent wherein a metal heat transfer surface is swaged or force fit toa metal heat transfer fluid conveyance is improved by applying to themetal to metal contact a low viscosity, penetrating, curable, reactive,film-forming, coating composition and curing the composition to therebyform an at least substantially continuous glass-like coating on saidheat transfer surface, said coating extending into voids and defectswhich may be present in said heat transfer surface, whereby a thermallyconductive corrosion protective layer is provided on said heat transfersurface. Preferably, the above described aqueous or non-aqueousoligomeric silane coating composition containing the silane of formula(1), silane condensation catalyst and solvent, and one or more optionalingredients, is applied to the interface of the metal-to-metal contactportions, whereby the oligomeric coating composition will displacegasses and liquids in the interface; and allowing the coatingcomposition to cure to a film thickness of from about 5 to about 150millionths of an inch, while also filling microvacancies in the metalsurfaces at the metal-to-metal contact interface.

[0055] The present invention also provides the coated heat exchangesurfaces and heat exchange systems and component parts, especially, finand tube heat exchange systems.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0056] The coating compositions used in the present invention maygenerally be characterized as low molecular weight oligomeric silanebased coatings. As used in this context the term “silane” is intended toinclude not only silanes but also silanols and siloxanes and the lowmolecular weight partial condensation products thereof. The term “lowmolecular weight” is intended to refer to the general absence of largeor bulky organic molecules or moieties as part of the silane components,namely, wherein the organic substituents are generally limited to loweralkyl groups, especially alkyl groups containing from 1 to 4 carbonatoms, especially, 1 to 3 carbon atoms, including, in particular,methyl, ethyl, n-propyl and iso-propyl groups, and aryl groups of nomore than about 8 carbon atoms, especially, no more than about 6 carbonatoms, such as, for example, phenyl, benzyl, and phenethyl.

[0057] Still further, the coating compositions of this invention arecharacterized by low viscosity to facilitate the penetration into themicrocrevices and microvoids present on the heat transfer surface. Asused herein, “low viscosity” is taken to mean the ability to penetrateinto micron and submicron size voids in metal surfaces. Typically, thecoating compositions of the present invention are characterized by acoating viscosity, measured using a No. 2 (#2) Zahn Cup, of from about 4to about 10 seconds, especially, from about 5 to about 8 seconds,measured at room temperature (approximately 18° C.).

[0058] The present invention also provides improved heat transfersystems coated with the subject silane based anticorrosion coatingcompositions as described herein. In particular, the invention coatingcompositions may be applied as protective coatings for new orrefurbished heat transfer systems and components as well as applied insitu to used, corroded or rusted heat transfer systems and componentparts thereof to significantly improve performance and increase theuseful life of the treated systems and component parts.

[0059] The compositions according to this invention are able to readilypenetrate into extremely small spaces and crevices, including down tonanometer inclusions in the indices of the metal substrates used tomanufacture heat exchange systems and component parts. As compared toconventional organic coatings, including known silane based coatingcompositions, the compositions of the present invention arecharacterized by low cohesive forces and, as a result, tend to wick intosuch small micro-spaces due to their active chemical nature. Thus, forexample, organic coatings, including acrylics, polyurethanes, epoxiesand phenolics, will not naturally wick into the small (e.g.,micro-voids) metal contact irregularities, even when applied byE-coating (electrocoating) techniques. While it has been suggested inthe art to mix some silane/siloxane compounds with acrylics, acrylicurethanes, organic acids and epoxides, however, these known formulationsare not able to take advantage of the small active molecules whichcharacterize the present compositions, which are capable of wicking intoextremely small voids in and between thermal contact surfaces.

[0060] The coating compositions used in the present invention arecapable of filling small nanometer size voids under driving forces ofcapillary action and Helmoltz free energy, displacing gasses and/orreacting with water or other chemicals. The ability of the coatingcompositions of this invention to migrate and penetrate capillarystructures releasing Helmoltz free energy allows them to displacemolecules bonded by means of secondary and tertiary valence forces andprovide protection by forming micron range thickness coatings, on theorder of from about 5 to about 150 millionths of an inch. These drivingforces even allow such penetration to occur under the high pressures,e.g., 2000 p.s.i., present injoints of such heat exchangers.Accordingly, the coating of the present invention are highly effectivefor increasing the efficiency of heat exchangers by providing parallelthermal paths between metal contact of, for example, heat dispersingfins and tubing or piping carrying fluids or gases for absorption ordispersion of heat.

[0061] The preferred low viscosity, penetrating, active coatingcompositions used in the present invention are silane based coatingcompositions, and may be may be aqueous or non-aqueous. Preferredcoating compositions are formed by admixing (a) at least one silane offormula (1)

R¹ _(n)Si(OR²)_(4−m)  (1)

[0062] where R¹ represents a lower alkyl group, a C₆-C₈ aryl group or afunctional group including at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional groups; with (b) a silanecondensation catalyst, which may be, for example, an acid, a base, ormixed acid-base. The silane(s) and catalyst are contacted in a lowviscosity solvent, typically a lower alkanol solvent, such as ethanol,isopropanol, and the like. One or more additional reactive or functionalingredients may be included in the composition.

[0063] Representative examples of suitable oligomeric silane coatingcompositions useful in the present invention have been described in myabove-identified patent and co-pending provisional applications and aredescribed briefly below.

[0064] I. an aqueous coating composition comprising a dispersion ofdivalent metal cations in lower aliphatic alcohol-water solution of thepartial condensate of at least one silanol of the formula RSi(OH)₃,wherein R is a radical selected from the group consisting of loweralkyl, or C₆-C₈ aryl or a functional group including at least one ofvinyl, acrylic, amino, mercapto, or vinyl chloride functional groups(e.g., 3,3,3-trifluoropropyl, γ-glycidyloxypropyl, andγ-methacryloxypropyl), at least about 70 percent by weight of thesilanol being CH₃Si(OH)₃, acid in amount to provide a pH in the range offrom about 2.5 to about 6.2, said divalent metal cations being presentin an amount of from about 1.2 millimoles to about 2.4 millimoles, permolar equivalent of the partial condensate, calculated as methyl silanesesquioxide;

[0065] II. an aqueous coating composition formed by admixing

[0066] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0067] wherein

[0068] R¹ is a lower alkyl group, a C₆-C₈ aryl group or anN-(2-aminoethyl)-3-aminopropyl group, and

[0069] R² is a lower alkyl group;

[0070] (B) an acid component selected from the group consisting ofwater-soluble organic acids, H₃BO₃ and H₃PO₃; and

[0071] (D) water;

[0072] III. a non-aqueous coating composition formed by admixing

[0073] (A) at least one silane of formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0074] wherein R¹ represents lower alkyl, C₆-C₈ aryl,3,3,3-trifluoropropyl, γ-glycidyloxypropyl, γ-(meth)acryloxypropyl,N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group;

[0075] R³ represents lower alkyl group; and

[0076] n is a number of 1 to 2; and

[0077] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide;and/or (iii) at least one metal alcoholate of formula (2)

M(OR³)_(m)  (2)

[0078] wherein M represents a metal of valence m,

[0079] R³ represents lower alkyl group; and

[0080] m is a number of 2, 3 or 4;

[0081] IV. a non-aqueous coating composition formed by admixing

[0082] (A) at least one silane of formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0083] wherein R¹ represents lower alkyl, C₆-C₈ aryl,3,3,3-trifluoropropyl, γ-glycidyloxypropyl, γ-(meth)acryloxypropyl,N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group;

[0084] R² represents lower alkyl or acetyl group; and

[0085] n is a number of 1 to 2;

[0086] (B) boric acid, optionally dissolved in lower alkanol;

[0087] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide;and/or (iii) at least one metal alcoholate of formula (2)

M(OR³)_(m)  (2)

[0088] wherein M represents a metal of valence m,

[0089] R³ represents lower alkyl group

[0090] m is an number of 2, 3 or 4; and,

[0091] (F) silica component selected from the group consisting of ethylortho-silicate, ethyl polysilicate and colloidal silica, dispersed inlower alkanol;

[0092] V. a non-aqueous coating composition formed by admixing

[0093] (A) at least one silane of formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0094] wherein R¹ represents lower alkyl, C₆-C₈ aryl,3,3,3-trifluoropropyl, γ-(meth)acryloxypropyl,N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group;

[0095] R² represents lower alkyl or acetyl group; and

[0096] n is a number of 1 to 2,

[0097] (A′) γ-glycidyloxypropyltrimethoxysilane;

[0098] (B) boric acid, optionally dissolved in lower alkanol;

[0099] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide;and/or (iii) at least one metal alcoholate of formula (2)

M(OR³)_(m)  (2)

[0100] wherein M represents a metal of valence m,

[0101] R³ represents lower alkyl group

[0102] m is an number of 2, 3 or 4;

[0103] VI. an aqueous coating composition formed by admixing

[0104] (A) at least one silane of formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0105] wherein R¹ represents lower alkyl, C₆-C₈ aryl, or a functionalgroup containing at least one of vinyl, acrylic, amino, mercapto, orvinyl chloride functional group; and

[0106] R² is a lower alkyl group;

[0107] (B) acid component comprising a member selected from the groupconsisting of water-soluble organic acids, H₃BO₃ and H₃PO₃; and

[0108] (D) water;

[0109] VII. an aqueous coating composition formed by admixing

[0110] (A) at least one silane of formula (1)

R¹ _(n)Si(OR²)_(4−n)  (1)

[0111] wherein R¹ represents lower alkyl, C₆-C₈ aryl, or a functionalgroup containing at least one of vinyl, acrylic, amino, mercapto, orvinyl chloride functional group; and

[0112] R² is a lower alkyl group;

[0113] (C) alkali component; and

[0114] (D) water;

[0115] VIII. an aqueous coating composition formed by admixing

[0116] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0117] wherein

[0118] R¹ represents lower alkyl group, C₆-C₈ aryl group or abifunctional silane containing vinyl, acrylic, amino, or vinyl chloridefunctional group; and

[0119] R² is a lower all group;

[0120] (E) (ii) colloidal aluminum hydroxide, (iii) metal alcoholate ofthe formula (2)

M(OR³)_(m)  (2)

[0121] wherein

[0122] M is a metal of valence m,

[0123] R³ is a lower alkyl group,

[0124] m is an integer of 3 or 4, or (iii) mixture of (ii) and (iii);and

[0125] (D) water;

[0126] IX. an aqueous coating composition formed by admixing

[0127] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0128] wherein

[0129] R¹ represents lower alkyl group, C₆-C₈ aryl group or abifunctional silane containing vinyl, acrylic, amino, or vinyl chloridefunctional group; and

[0130] R² is a lower alkyl group;

[0131] (D) water;

[0132] (G) chromium acetate hydroxide; and

[0133] (H) lower alkanol;

[0134] X. an aqueous coating composition formed by admixing

[0135] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0136] wherein

[0137] R¹ represents lower alkyl group, C₆-C₈ aryl group or a functionalgroup including at least one of vinyl, acrylic, amino, mercapto, orvinyl chloride functional group; and

[0138] R² is a lower alkyl group;

[0139] (D) water;

[0140] (E) (ii) colloidal aluminum hydroxide, (iii) metal alcoholate ofthe formula (2)

M(OR³)_(m)  (2)

[0141] wherein

[0142] M is a metal of valence m,

[0143] R³ is a lower alkyl group,

[0144] m is an integer of 3 or 4, or (iii) mixture of (ii) and (iii);

[0145] (F) alkali metal silicate, which may be hydrolyzed; and

[0146] (H) lower alkanol.

[0147] XI. a non-metallic aqueous coating composition formed by admixing

[0148] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0149] wherein

[0150] R¹ represents lower alkyl group, C₆-C₈ aryl group or a functionalgroup including at least one of vinyl, acrylic, amino, mercapto, orvinyl chloride functional group; and

[0151] R² is a lower alkyl group;

[0152] (A″) 3-(2-aminoethylamino)propyltrimethoxysilane or3-aminopropyltrimethoxysilane;

[0153] (D) water;

[0154] (H) lower alkanol; and

[0155] (I) epoxide silane;

[0156] XII. an aqueous coating composition formed by admixing

[0157] (A) at least one silane of the formula (1)

R¹Si(OR²)₃  (1)

[0158] wherein

[0159] R¹ represents lower alkyl group, C₆-C₈ aryl group or a functionalgroup including at least one of vinyl, acrylic, amino, mercapto, orvinyl chloride functional group; and

[0160] R² is a lower alkyl group;

[0161] (B) boric acid;

[0162] (C) at least one alkali component comprising an hydroxide orcarbonate of divalent metal;

[0163] (D) water;

[0164] (H) lower alkanol, and

[0165] (J) ethyl polysiloxane.

[0166] As examples of silanes of formula (1), wherein R¹ is an alkylgroup or aryl group, mention may be made of, for example,methyltimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, n-butyltrimethoxy silane, isobutyltrimethoxy silane,phenyltrimethoxy silane, preferably methyltrimethoxy silane. In the casewhere R¹ is a functional group, mention may be made, for example, ofN-(2-aminoethyl)-3-aminopropyltrimethoxy silane,3-mercaptopropyltrimethoxy silane, 3-mercaptopropyltriethoxy silane,3-aminopropyltriethoxy silane, 3-(meth)acryloxypropyl trimethoxy silane,3-(meth)acryloxypropyltriethoxy silane, n-phenylaminopropyltrimethoxysilane, vinyltriethyoxy silane, vinyltrimethoxy silane, allyltrimethoxysilane, and any of the aminosilane catalysts, described herein below.

[0167] As used herein, the expression “functional group” is intended toinclude any group, other than hydroxyl, (including alkoxy, aryloxy,etc.), which is hydrolyzable to provide, in situ, a reactive group(e.g., reactive hydrogen) which will react, in other than a condensationreaction, with the substrate (e.g., metal), itself, or other reactivecomponents in or from the coating composition.

[0168] The functional groups, in addition to the hydroxyl group (byhydrolysis of the (OR²) groups), tend to form three-dimensional orcross-linked structure, as well known in the art.

[0169] Moreover, in the various embodiments of the invention, it isoften preferred to use mixtures of two or more silane compounds offormula (1). Mixtures of at least phenyltrimethoxysilane andmethyltrimethoxysilane are often especially preferred.

[0170] Generally, total amounts of silane compounds of formula (1) willfall within the range of from about 40 to about 90 percent by weight,preferably from about 50 to about 85 percent by weight, based on thetotal weight of silanes, catalyst(s) and solvent(s).

[0171] In addition to silane compound(s) of formula (1), the compositionmay additionally include a bistrifunctional aminosilane, such asrepresented by the following formula (4):

X[R¹Si(OR²)₃]₂  (4)

[0172] where R¹ and R² are as defined above, and X represents an aminogroup (—NH) or keto group

[0173] as a basic catalyst, not requiring acid stabilization. As arepresentative example of aminosilane or ketosilane catalyst accordingto formula (4), mention may be made of, for example,bis(trimethoxypropylsilane) amine, bis(trimethoxyethylsilane) amine,di(trimethoxybutylsilane) ketone, di(trimethoxypropylsilane) ketone, andthe like. The silane compounds of formula (4) function as a less activebasic catalyst, not requiring acidic passivation. Minor amounts, usuallyfrom about 1 to about 10 parts, preferably, from about 2 to about 8parts, of compound of formula (4) per 100 parts of silane compound(s) offormula (1) provide satisfactory results.

[0174] The silane condensation catalyst (b) may be, for example, a baseor alkali component. As examples, an inorganic base, such as, forexample, calcium hydroxide, aluminum hydroxide or zinc hydroxide, ormixture thereof; or an organic base component, such as, for example,aminosilane, may be mentioned.

[0175] The amount of the base catalyst is generally, up to about 2%,such as, for example, from about 0.1 to 2.0%, by weight of thecomposition, especially, from about 0.2 to 1.6%.

[0176] The silane condensation catalyst (b) may also be, for example, anacid. As examples of the acid catalyst component (b), mention may bemade of lower alkanoic acids, such as, for example, formic acid, aceticacid, propanoic acid, butyric acid, and inorganic acids, such as, forexample, boric acid (H₃BO₃) or ortho-phosphorous acid (H₃PO₃),preferably acetic acid, boric acid or ortho-phosphorous acid, mostpreferably, for reasons of economy and safety, acetic acid. The acid maybe added as free acid or as inorganic salt thereof, such as alkali metal(e.g., sodium), alkaline earth metal (e.g., calcium), or ammonium salt.

[0177] Generally, total amounts of the inorganic acid component willfall within the range of from about 0.3 to about 4 percent by weight,preferably from about 0.5 to about 3%, preferably, from about 0.5 toabout 2.5 percent by weight, based on the total weight of silanes, acidcomponent and water. For acetic acid, the preferred range is from about0.1 to about 1.0 percent, preferably, from about 0.2 to about 0.7percent, by weight, based on the total weight of the composition.

[0178] Of course, one or more other silanol condensation catalysts, aswell known in the art, may be used in place of or in addition to theacid and/or base catalyst.

[0179] As examples of organic solvents (c), mention may be made of loweralkanol, e.g., C₂-C₄ alkanols, preferably isopropanol.

[0180] Generally, total amounts of organic solvent, such as, loweralkanol, will fall within a range of from 10 to about 50 percent byweight, preferably from 15 to about 40 percent by weight, based on thetotal weight of silane(s), acid component and/or base component andwater. In some cases, however, substantially higher amounts may beconvenient, especially where, for example, the coating compositions areapplied, usually by spraying, to preexisting HVAC systems, such as, forexample, evaporators, or other structures wherein ready access tocomponent parts and/or to metal-metal heat transfer junctions, may beinhibited due to tight fits, etc.

[0181] Where it is deemed to be advantageous or necessary to provideespecially dilute coating compositions, for example, amounts of alcoholsolvent from about 40 to about 90% by weight, or more, especially, fromabout 50 or 60% by weight or higher, based on the total composition, itis often advantageous, to provide a portion of the solvent as a separatecomponent to be added to the remainder of the composition after mixingof the silane(s) and silane condensation catalyst(s). In such case, thesystem may be provided as a two or three “pot” system, e.g., silanecompound(s) in one pot, catalyst(s) in a second pot, a portion ofalcohol solvent, e.g., isopropanol, with one or both of the first andsecond pots, and the remainder of the alcohol and/or water solvent in athird pot.

[0182] The coating compositions of this invention may be non-aqueous oraqueous. When water, as component (j), is present, the total amount ofwater will generally fall within the range of from about 10 to about 60percent by weight, preferably from about 10 to about 45 percent byweight, based on the total weight of (a) silane(s), (b) catalystcomponent(s), (c) organic solvent, (j) water, (k) co-solvent.

[0183] Some or all of the water may be provided by the acid and/or basecomponent, when the base or acid component is supplied as an aqueoussolution, e.g., 5% aqueous solution of ortho-phosphorous acid orsaturated aqueous solution of boric acid (about 6% by weight of H₃BO₃).

[0184] Since the presence of metallic and other impurities may have anadverse effect on the properties of the resulting coatings, preferably,water, when used, is distilled or deionized water.

[0185] According to a particularly preferred embodiment of the presentinvention, the coating compositions may include metal catalysts whichadditionally provide a tint or coloration to the resulting coating.Chromium acetate hydroxide is especially useful in this regard, servingas a basic catalyst which provides a bluish tint to the resultingcoating. This feature may be especially useful, for example, inconnection with providing corrosion resistant coatings to HVAC systemshaving large surface areas and/or difficultly accessible regions, wherevisibility of the applied coating can assure total coverage of the areasto be coated while avoiding wasting coating by excessive applicationsover already coated surfaces.

[0186] Other basic metal catalysts providing a colorant functioninclude, for example, iron acetate, iron acetate hydroxide, chromiumacetate, and the like. Other metal compounds such as compounds ofantimony, lead, barium, etc., also form colored products, but tend to bemore toxic and, therefore, less useful for general purposes.

[0187] The present coating composition may be formed by mixing theabove-noted components and allowing them to react. A suitable reactiontime is typically 4 to 12 hours, if no colloidal aluminum hydroxideand/or metal alcoholate is present. Shorter reaction times may beobtained in the presence of colloidal aluminum hydroxide and/or metalalcoholate.

[0188] For ease of handling, the coating composition may be provided asa two or three container system, e.g., the silane component and anysilicate component, if present, being provided in a first container andall other components being provided in a second or second and thirdcontainer. Water, when included in the composition, may be providedseparately from the other components. The contents of the two or three(or more) containers may be mixed shortly prior to use and allowed toreact for an appropriate reaction time, as noted above.

[0189] While general and preferred ranges of amount for thefilm-forming, catalytic and solvent components have been describedabove, it will be recognized by those skilled in the art, that theseamounts may be increased or decreased as necessity demands and that theoptimum amounts for any particular end use application may be determinedby the desired performance and HVAC system to be coated, including typeof system and location. In this regard, for example, when the amount ofcatalyst is reduced, the time to achieve freedom from tack willincrease. Similarly, when the amount of the catalyst(s) is (are)increased, this may lead to increased rates of cracking, loss ofadhesion and performance loss of the resulting coating.

[0190] The compositions of this embodiment may further include one ormore additional additives for functional and/or esthetics effects, suchas, for example, (d) colloidal aluminum hydroxide, (e) metal alcoholate,(f) silica and/or silicates, (g) color forming silanol condensationcatalyst, (h) epoxide silane, (i) ultraviolet absorber, (j) water, (k)cosolvent, and the like.

[0191] The above-noted optional ingredients may be used singly or in anycombination in the coating composition of this invention.

[0192] As examples of silicate component (f), mention may be made ofethyl or methyl orthosilicate or ethyl polysilicate. These silicates maybe hydrolyzed, for example, from about 28% to about 52% silica.Especially preferred in this regard is tetraethylsilicate (TEOS) (oftenreferred to simply as ethyl silicate) which has been subjected tocontrolled hydrolysis, providing a mixture of TEOS and, from about 20%to about 60% polydiethoxysilane oligomers. For example, a 50% hydrolysisproduct may be referred to herein as “polydiethoxysilane (50%).”

[0193] Generally, total amounts of silicate component, when used, willfall within the range of from 0 to about 45 percent by weight,preferably from 0 to about 25 percent by weight, based on the totalweight of silanes, acid component and water.

[0194] As example of (k) co-solvent, mention may be made, for example,of mono-lower alkyl ether of alkylene (e.g., ethylene) glycol, such as,mono-C₁-C₆-alkyl ethers of ethylene glycol, for example, monomethylether, monoethyl ether, monopropyl ether, monobutylether,monopentylether or monohexylether, preferably monoethyl ether ofethylene glycol. Other known and conventional co-solvents may also beused, for example, acetone, ketones (e.g., methylethylketone, ethers(e.g., ethylether), esters (e.g., ethyl acetate), and the like. Theco-solvents should also have low viscosity, e.g., lower than that ofwater, preferably, less than about 8 centipoise.

[0195] Generally, total amounts of the mono-lower alkyl ether ofethylene glycol or other co-solvent, when used, will fall within therange of from 0 to about 15 percent by weight, preferably from 0 toabout 6 percent by weight, based on the total weight of silanes, acidcomponent and water. However, in the event that one of the low viscositysolvents, e.g., methylethylketone, is used as the main solvent, the sameamounts as discussed above for the preferred alcohol solvents, may beused.

[0196] As an example of (i) ultra-violet light absorber, mention may bemade of titanium dioxide in finely powdered form, e.g., having anaverage particle diameter of about 20 nm. Other inorganic or organicultra-violet light absorbers may be utilized in so far as they do notinterfere with the objects of this invention.

[0197] Generally, total amounts of the ultra-violet light absorber, whenused, will fall within the range of from 0 to about 10 percent byweight, preferably from 0 to about 5 percent by weight, based on thetotal weight of silanes, acid component and water.

[0198] Metal catalysts, such as, for example (d) colloidal aluminumhydroxide, and/or (e) metal alcoholates, such as those represented bythe following formula (2):

M(OR³)_(m)  (2)

[0199] where M is a metal of valence m (namely, from Groups IIIA, IVA,IIB or IVB of the periodic table of the elements), e.g., boron,titanium, aluminum, indium, yttrium, cerium, lanthanum, silicon, tin,hafnium, etc. and R³ is a lower alkyl group, e.g., C₁-C₆ straight orbranched chain alkyl group, preferably C₂-C₄ alkyl group, mostpreferably, isopropyl, isobutyl or n-butyl; and m is an integer of 3 or4, may also be used. Boron, aluminum and titanium are especiallypreferred as metal M because the alkoxides of these metals are morereadily commercially available, and tend to be non-toxic).

[0200] As specific examples of the metal alcoholates of formula (2),mention may be made of titanium alcoholates of C₂-C₄ alkanols, e.g.,titanium tetraisopropoxide and titanium tetrabutoxide.

[0201] In addition, double metal alcoholates of, for example, AlTi,AlZr, AlY, MgAl, MgTi, MgZr, etc., may also be used.

[0202] The presence of the trivalent and tetravalent metal ions areespecially useful for coating compositions applied to steel since theytend to form insoluble (water and alkali) iron silicates, whereas theproducts of divalent metals, tend to be soluble.

[0203] Generally, total amounts of the colloidal aluminum hydroxideand/or metal alcoholate, when used, will fall within the range of from 0to about 2.5 percent by weight, preferably from 0 to about 1 percent byweight, based on the total weight of (a) silane(s), (b) acid and/or basecomponent(s) and solvent(s).

[0204] Within the above general proportions, and based on the weight ofthe entire composition, the amount (parts by weight) of the individualclasses of ingredients, will usually fall within the following ranges:silane component (a) from about 15 to about 25 parts, preferably, as amixture of from about 15 to about 20 parts of methyltrimethoxysilane andfrom about 1 to about 5 parts of phenyltrimethoxysilane;

[0205] base component condensation catalyst (b), when present, fromabout 0.1 to 3 parts, preferably from about0.2 to 2.5 parts; acidcomponent condensation catalyst (b), when present, from about 0.2 toabout 0.8 part: solvent. e.g.. isopropyl alcohol, to provide theappropriate viscosity, generally, from about 5 to about 60 parts.preferably, from about 10 to about 40 parts: water (j), when present,from about 2.5 parts by weight to about 40 parts: silicate component(f), when used, from 0 to about 15 parts by weight: mono-lower alkylether of ethylene glycol and/or other co-solvent (k), when used, from 0to about 3 parts; ultra-violet light absorber (i), when used, from 0 toabout 2 parts by weight: colloidal aluminum hydroxide and/or the metalalcoholate, when used, from 0 to about 0.5 part by weight.

[0206] Furthermore, the above general and preferred amounts of therespective ingredients apply equally to the various embodiments I-XII,of the coating compositions, as identified above.

[0207] Moreover, on some occasions it has been observed that theactivity of the coating compositions is so high that when applied toothickly, a random distribution of lumps, presumably due to gelling, mayform. Such lumps, if present, can serve as corrosion initiation centers.Accordingly, one skilled in the art will recognize that the coatingcompositions according to this invention should preferably be applied inthe minimum amount necessary to substantially completely coat thesurface to be protected. Coating thicknesses of less than 1 mil.preferably, less than about 0.5 mil, are usually satisfactory.

[0208] Heat exchange devices often use a swaged metal to metal jointfrom fin to tube/pipe, made by hydraulically or physically expanding thetube/pipe to force intimate metal to metal contact for heat transferfrom fin to joint. However, whether or not exacerbated by imperfectionsin the expansion techniques/equipment, or/and as a result of corrosion,the presence of micro-voids are inherent in such metal to metal contact.In accordance with the present invention, these micro-voids are filledby the new chemically active coating compositions described herein,thereby providing more efficient parallel heat paths as well ascorrosion protection, not heretofore possible. Accordingly, theefficiencies of both new and used heat exchange apparatus issignificantly increased while extending the useful service life of theapparatus. However, it is noted that the relative increases inefficiency are substantially higher for older and corroded systems,often on the order of 20% to 60% or even 80% or more improvements inefficiencies and reduction in operating costs, as compared to moremodest, but substantial improvements, on the order of from about 1 to4%. or higher, for new (e.g.. OEM) HVAC systems and/or components. Atthe same time, however, by applying the coatings of the presentinvention to new or old HVAC systems and/or component parts, long termreductions in maintenance requirements and associated costs areachievable.

[0209] Organic coatings, such as epoxies, have a thermal conductivitygenerally about one hundredth the thermal conductivity of ametal-to-metal contact surface. Even with metal or other conductivefillers, which tend to have a short life from corrosion from molecularlevel water permeation, organic coatings are two orders of magnitudeless conductive than metal-to-metal contact. Silicone or glass-likecoatings formed according to the present invention, on the other hand,are generally less than 5 to 10 times less conductive than themetal-to-metal contact. However, the significant and unique ability ofthese coatings to penetrate metal-to-metal nano-voids created by theirregular microsurface profile of metals allows the coatings to fill asignificant amount of void space in such metal-to-metal joint (e.g.,fin-tube/pipe) and, while providing less conductivity, and offers asignificant, parallel path for thermal conductivity.

[0210] Therefore, even for a corroded metal-to-metal thermal joint,e.g., a fin and tube structure, a significant improvement in thermaltransfer efficiency will be achieved.

[0211] Often, electrolytes will react with metals or crystallize withsuch a thermal joint and create salts, other crystalline corrosionstructures, or corrosion by-products that expand as they are formed withpressures as high as 2000 pounds per square inch. This causes the amountof contact in a metal to metal heat transfer joint, as described herein,to have less contact then when manufactured, or in some cases, virtuallyno direct contact due to air or corrosion by-products remaining betweenmetal surfaces.

[0212] This problem is substantially completely avoided by the presentinvention since the subject coating compositions, in addition todisplacing gasses, form bonds to the corrosion products, includingchemical bonds to oxides, medium to strong hydrogen bonds toelectrolytes, thereby dissolving the corrosion products, and/orencapsulating/filling and providing parallel thermal path(s) around thecorrosion products. As a result, heat exchangers otherwise operating atlow efficiencies due to corrosion, joint expansion and the like, willundergo a significant and substantial improvement in thermalconductivity as a result of the coating treatment according to thisinvention.

[0213] Again, while not wishing to be bound by any theory of operation,it is believed that the effectiveness of the instant classes ofsilane/siloxane coating compositions arises from the ability of suchcoatings to form dendritic interfacial linkages that effect theirperformance in thin layers, normally about 5 to about 150 millionths ofan inch.

[0214] Therefore, notwithstanding low thermal conductivities of thesilane coatings, per se, due to the extremely thin nature of thedeposited coatings, only an insignificant and negligible thermal lossoccurs, in contrast to the thermal transfer gains by the parallel pathfor heat exchange.

[0215] Moreover, for new/original manufactured and/or refurbishedexchangers, a 10 to 40% increase in surface conducting area is achievedby application of the present coatings (with thermal conductivities 5 to10 times less than metal-to-metal contact) in a metal-to-metal joint.This will, therefore, produce an overall cooling/power reductionefficiency increase of usually from about 1 to about 10%.

[0216] The overall corrosion protection provided according to thisinvention, either within the metal-to-metal joint, which is effectivelyfilled and rendered unavailable for penetration of electrolytes or othercorrosive gases or chemicals; or on other heat transfer surfaces incontact with air, water, or conductive structure or media/chemical orconveyance (e.g., tube, pipe, conductive metal sink, etc.) for fluid orgases passed through the exchanger; are all protected with a doublecorrosion protection not offered by normal organic coatings. The instantcoating compositions are effective, for example, in eliminating “whiterusting” problems resulting from growth of zinc oxide on brass or otherzinc-containing metals or alloys. In the present invention, the zinc andzinc oxide will be effectively brought into the polymeric matrix coatingto not only eliminate further growth of the zinc oxide but enhancing thestrengthening of the coating.

[0217] Coatings formed using the subject oligomeric silane based coatingcompositions, applied to metal surfaces and wiped off until only theareas of bonding remains, 5 to 20 millionths of an inch, form coatedmetal surfaces able to pass 700 to 1000 hours in as ASTM B-117 saltspray test. If the coating is allowed to grow the dendritic glassstructures to about 150 millionths of an inch the combination of thebond and glasslike coating growth enables the coated metal surface topass 4000 to 6000 hours in the same ASTM test.

[0218] Thus, a double protection is afforded the heat exchangers treatedin accordance with the present invention.

[0219] The present invention may be applied to any type of heat exchangesystem and the component parts thereof. For example, mention may be madeof evaporator and condensing coils in HVAC systems, radiators fordispelling or absorbing heat, exchangers with dissimilar or similarmetals, refrigeration exchangers, and the like. A particularly preferredtype of heat exchange system is the fin and tube type. Heat exchangerscoated according to the present invention will maintain highefficiencies, equivalent or superior to new, uncoated exchangers, due toexclusion of electrolytes that would normally form corrosion products inmetal contact areas, thereby retarding corrosion due to the dual surfacechemical bond and coating structure formed on surfaces and in smallinclusions in joints, not accessible with previously known coatingmaterials.

[0220] The anticorrosion silane-based oligomeric coating compositions ofthis invention may be applied to confer protection on all heat transfersurfaces that come into contact with air, water, or conductive structureor media/chemicals, including, conveyances (e.g., tubes, pipes,conductive metal sinks, etc.) for liquid or gasses passing through theexchanger. For example, the present invention may be applied to coat newor used heat exchangers and all other components of air-conditioners andchillers, and other refrigeration devices, including cabinets,components, compressors, tubing, piping, grills, fans, motors, externalelectrical conduits, coated and uncoated wiring, switch boxes, and theassociated nuts, bolts, and other connectors.

[0221] The coating compositions of this invention may be applied to newor used/corroded heat exchangers, made of similar or dissimilar metals,wherein heat transfer fluids or gasses flow in tubing, piping, or otherforms of heat conveyance, which are swaged or expanded (e.g., force fitmetal joints) to metal to metal contact with other heat exchangersurfaces, and cooled by, for example, air, water, conductive metal heatsink, etc., to increase efficiency of heat transfer of the heatexchanger by improving the metal to metal joint transfer by increasingthe contact area between the similar or dissimilar metals. As a resultof the improved efficiency, energy costs for running the coated units,e.g., air-conditioning condenser; condenser/chiller; will besubstantially lowered.

[0222] The coated substrates of the HVAC systems and/or component parts,whether new or used/corroded, by virtue of the chemical bonding andsilica or siloxane bonding, with the additional dendritic linkages,producing a glass-like structural formation over the chemical bond area,reduces the available chemical activity on the coatedsurfaces/interfaces of the metal or metal to metal, to thereby provide a“double” protection. This protection is provided on all heat transfersurfaces in contact with air, water, or conductive structure ormedia/chemicals; as well as on the conveyances (tubes, pipes, conductivemetal sinks, etc.) for fluid or gases which pass through the exchanger.

[0223] In this regard, by filling the microvoids and macrovoids withinthe metal to metal joints, the metal becomes unavailable for penetrationof electrolytes or corrosive gases or chemicals.

[0224] In addition, in view of the hydrophobic nature of the appliedcoatings, the coated surfaces will stay cleaner for longer periods oftime, thereby affording significant and substantial savings inmaintenance costs.

[0225] Moreover, in accordance with a particular feature of the presentinvention, even when corrosion protection is not of paramountimportance, the coated HVAC systems and component parts according to thepresent invention are characterized by being non-adherent to varioustypes of soiling agents and to microbial growths. Accordingly, thecoated articles of the present invention have the additional advantageof requiring less frequent maintenance (e.g., cleaning) and, since theydo not promote growth of microorganisms, e.g., fungi, mold spores,yeast, bacteria, and the like, are advantageous for use in protectingHVAC systems used to heat/cool occupied structures, e.g., offices,factories, and the like. That is, since growth of microorganisms isinhibited, when the HVAC systems and component parts thereof, e.g.,evaporators, flow ducts, and the like, are treated in accordance withthe present invention, subsequent introduction of microorganisms intothe structures which are heated/cooled by the coated systems is greatlyinhibited or prevented.

[0226] The invention will now be illustrated by the followingnon-limiting examples. It is understood that these examples are given byway of illustration only and without intent to limit the inventionthereto.

Referential Example 1A

[0227] Calcium hydroxide (1 millimole) is added to 20 part watercontaining 0.3 grams glacial acetic acid. The initial pH is about 4.2.The acetic acid catalyst and the calcium hydroxide should react to formcalcium acetate. In a separate container 20 parts ofmethyltrimethoxysilane is mixed with 20 parts isopropyl alcohol. Whilethe silane alcohol mixture is being stirred, the aqueous solution isslowly added. The composition is allowed to react for about 3 hours. Theresulting mixture (oligomeric coating composition) has a viscosity ofabout 8 seconds, using a #2 Zahn cup, and is ready for application. Thesolids level of the composition is about 16%, based on sesquioxidecontent.

Referential Example 1B

[0228] The procedure of Referential Example 1A is repeated except thatthe 20 parts of methyltrimethoxysilane is added to 40 parts of isopropylalcohol.

Referential Example 2

[0229] The procedure of Referential Example 1 is repeated, except thatthe amount of calcium hydroxide is changed from 1 millimole to 0.7millimole.

Referential Example 3

[0230] The procedure of Referential Example 1 is repeated, except thatthe amount of calcium hydroxide is changed from 1 millimole to about 2.4millimoles.

Referential Example 4

[0231] The procedure of Referential Example 1 is repeated, except thatin place of calcium hydroxide, an equivalent amount of calcium oxide isused.

Referential Example 5

[0232] The procedure of Referential Example 1 is repeated, except thatin place of calcium hydroxide, an equivalent amount of magnesiumhydroxide is used.

Referential Example 6

[0233] The procedure of Referential Example 1 is repeated, except thatin place of calcium hydroxide, an equivalent amount of zinc oxide isused.

Referential Example 7

[0234] The procedure of Referential Example 1 is repeated, except thatin place of calcium hydroxide, a mixture of calcium hydroxide and zincoxide is used.

Referential Example 8

[0235] The procedure of Referential Example 1 is repeated, except that,0.4 parts 20 nanometer TiO₂, and 0.15 parts of hydroxybenzoylphenone,are added to the coating composition.

Referential Example 9

[0236] The procedure of Referential Example 1 is repeated, except thatinstead of using 20 parts of methyltrimethoxysilane and 20 partsisopropyl alcohol, a mixture of 18 parts methyltrimethoxysilane,2.5parts γ-glycidyloxypropylsilane and 1.9 parts phenyltrimethoxysilane and20 parts isopropyl alcohol is used.

Referential Example 10

[0237] In a first container containing 20 parts isopropyl alcohol,methyltrimethoxysilane, phenyltrimethoxysilane andpropyltrimethoxysilane are mixed in amounts of 15 parts, 1 part and 5parts, respectively. In a second container,aminoethylaminopropyl-trimethoxysilane{N-(2-aminoethyl)-3-amino-propyltrimethoxysilane}, water, acetic acid,and titanium dioxide (average particle size, 22 nm), are mixed inamounts of 0.2 part, 13 parts, 0.4 part, and 0.2 part, respectively.After combining the contents of the two containers, the resultingmixture is allowed at least four hours to homogenize. Fasterhomogenization will be achieved by using a mechanical shaker or stirrer.

Referential Example 11

[0238] In a first container containing 10 parts isopropyl alcohol,phenyltrimethoxysilane, methyltrimethoxysilane and tetrabutoxytitanateare mixed in amounts of 5 parts, 15 parts and 0.3, 0.4, 0.5 or 0.6 part,respectively. In a second container, isopropyl alcohol and an aqueous 3%boric acid solution are mixed in amounts of 13 parts and 13 parts,respectively. After combining the contents of the two containers, theresulting mixture is ready for application after about three hours.

Referential Example 12

[0239] 10 parts of a 3% boric acid solution are placed in a firstcontainer. 20 parts of methyltrimethoxysilane, 10 parts of isopropylalcohol and 0.5 part of tetrabutoxy titanate are mixed in a secondcontainer. The contents of the two containers are mixed together andallowed to react to form a coating composition.

Referential Example 13

[0240] 20 parts of methyltrimethoxysilane, 10 parts of isopropyl alcoholand 0.2 parts of magnesium ethoxide are mixed until the solution becomeshomogeneous. To this solution a base catalyst (a saturated solution of amixture of calcium hydroxide, calcium carbonate and magnesium carbonate,diluted with 2 parts water), is added. The resulting formulation isallowed to react for about 1 hour.

Referential Example 14

[0241] After thoroughly mixing 20 parts methyltrimethoxysilane with 10parts isopropyl alcohol,0.2 parts ofaminoethylaminopropyltrimethoxysilane is added to the resultingsilane-alcohol mixture, and again thoroughly mixed. Then 6 parts ofwater is added to the resulting mixture and, after standing for 90minutes, the composition is ready for use.

Referential Example 15

[0242] 20 parts of methyltrimethoxysilane and 20 parts isopropyl alcoholare mixed and the resulting mixture is combined with 0.25 parts ofaluminum isopropoxide under stirring until the aluminum isopropoxide ispartially dissolved. To this mixture 6 parts water is added. Afterstirring for about one hour, the mixture is ready to be applied.

Referential Example 16

[0243] This example shows the use of a double metal alkoxide catalystfor the silane coating composition. A uniform solution, obtained bymixing 15 parts methyltrimethoxysilane, 5 parts phenyltrimethoxysilane,20 parts isopropyl alcohol, and 2 parts polydiethoxysiloxane (˜50%solids) is catalyzed with 6 parts of an alcoholic (isopropyl alcohol)solution of a double alkoxide of aluminum and titanium. The resultingmixture is allowed to react for about 4 hours using six parts water.

Referential Example 17

[0244] To a mixture formed by combining 20 parts methyltrimethoxysilane,20 parts isopropyl alcohol, and 2 parts polydiethoxysiloxane (˜52%solids), there is added a catalyst containing 0.6 parts boron ethoxideand 0.2 parts aluminum isopropoxide. After the solids are dissolved,water (6 parts) is added to complete the catalysis. The resultingmixture is allowed to stand (react) for about 1 hour.

Referential Example 18

[0245] 20 parts methyltrimethoxysilane, and 20 parts isopropyl alcohol,are mixed with 0.2 parts of aminoethylaminopropyltrimethoxysilane (ashydrolysis catalyst). After thoroughly mixing with 6 parts water, themixture is allowed to react (hydrolyze) for 45 minutes. Then, themixture is combined with 0.3 parts phenyltrimethoxysilane predispersedin 10 parts isopropyl alcohol. After about 1 hour, the composition isready to be applied.

Referential Example 19

[0246] Twenty (20 ) parts methyltrimethoxysilane, 5 partsphenyltrimethoxysilane and 20 parts isopropyl alcohol are combined andthoroughly mixed. To this mixture is first added 0.2 parts of boric acidfollowed by addition of 4 parts of polydiethoxysiloxane (50%). After theboric acid is dissolved, 0.6 parts tetrabutoxy titanate and then 6.5parts water are added. By adding the water slowly, premature hydrolysisof the tetrabutoxy titanate may be prevented. After about one hour, 1.6parts of a 0.5% solution-suspension of calcium hydroxide in isopropylalcohol is added and the mixture is allowed to react for at least onehour and is then ready for application.

Referential Example 20

[0247] To a container containing 10 parts of polydiethoxysiloxane (˜50%)is added 20 parts of isopropyl alcohol and 0.2 parts of aluminumisopropoxide, followed by 5 parts of phenyltrimethoxysilane. The mixtureis stirred until it becomes clear. At that time, while continuingstirring, 2.3 parts of water are added, followed by 5 parts ofphenyltrimethoxysilane. After stirring for about 3 hours, the mixturemay be applied.

Referential Example 21

[0248] To a container containing 10 parts of polydiethoxysiloxane(approx. 50%) is added, while stirring, 20 parts of isopropyl alcoholand 0.1 part of boric acid. Stirring is continued until the solutionbecomes clear. Then, 0.2 parts of titanium tetrabutoxy oxide are added.The mixture is stirred for about 3 hours. Then, 2.3 parts of water areadded, while stirring, followed by 5 parts of phenyltrimethoxysilane.After stirring for an additional about 3 hours, the solution may beapplied.

Referential Example 22

[0249] 200 parts methyltrimethoxysilane and 100 parts isopropyl alcoholare mixed in a first container (Container A). Separately, in ContainerB, 40 parts of a saturated solution of calcium hydroxide is diluted with20 parts of water before the diluted solution is added to Container A.

[0250] In Container C, 6.2 parts boric acid is dissolved in 96.8 partsof isopropyl alcohol and is then combined after cooling begins, with thecontents of Container A (to which the contents of Container B has beenadded).

[0251] After about three days, the resulting mixture forms a sprayableor wipable coating composition.

Referential Example 23

[0252] 20 parts each of methyltrimethoxysilane and isopropyl alcohol aremixed in a first container, Container A. Then, 0.3 part of boric acid isadded, followed by addition of 0.2 to 0.3 part of tetrabutyl titanate toassist in the solubilization of the boric acid catalyst. Finally, 10 to20 parts of water are slowly added since the reaction is exothermic.After a few minutes, the mixture will warm up and is ready to beapplied.

Referential Example 24

[0253] In a first container, isopropyl alcohol, methyltrimethoxysilane,phenyltrimethoxysilane and isobutyltrimethoxysilane are mixed in amountsof 10 parts, 15 parts by weight, 1 part by weight and 5 parts by weight,respectively. In a second container,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, water, acetic acid,ethylene glycol monoethyl ether and titanium dioxide are mixed inamounts of 0.2 part by weight, 13 parts by weight, 0.4 part by weight, 3parts by weight and 0.2 part by weight, respectively. After combiningthe contents of the two containers, the resulting mixture is allowed atleast four hours to homogenize. The so-formed liquid mixture is ready tobe applied.

Referential Example 25

[0254] 5 parts by weight of phenyltrimethoxysilane are added to acontainer containing 15 parts by weight of methyltrimethoxysilane. Whilemixing, 0.3 part by weight of tetrabutoxytitanate are added, along with15 parts by weight of ethyl polysilicate, which has been hydrolyzed to40% silica, and 15 parts by weight of isopropyl alcohol. After mixing,13 parts by weight of an aqueous 6% boric acid solution are added and,after waiting eight hours, the resulting mixture is ready to be applied.

Referential Example 26

[0255] 5 parts by weight of phenyltrimethoxysilane and 2 parts by weightof γ-glycidyloxypropyltrimethoxysilane are added to a vessel containing15 parts by weight of methyltrimethoxysilane and mixed. While mixing,0.4 part by weight of tetraisopropyoxytitanate in 20 parts isopropylalcohol is added. The resulting nonaqueous composition is ready to beapplied.

Referential Example 27

[0256] To a vessel containing 15 parts by weight ofmethyltrimethoxysilane and 15 parts isopropyl alcohol, there is added,while stirring, 5 parts by weight of phenyltrimethoxysilane. To theresulting mixture, while continuing stirring, 0.2 part by weight oftetrabutoxytitanate is added, followed by 4 parts by weight of ethylpolysilicate (hydrolyzed to 40% silica), and 0.2 part by weight ofvinyltriacetoxysilane. The resulting composition is ready to be applied.

Referential Example 28

[0257] This formulation illustrates a coating composition which is shownformulated as a three container system (i.e., water; silane/alcohol;catalyst).

[0258] In one container a mixture of 20 parts of methyltrimethoxysilaneand 20 parts isopropyl alcohol is provided. While the silane-alcoholmixture is being stirred, 20 parts water is added. After thoroughlymixing, 1 part of an amine stabilized titanium catalyst (e.g., Tyzor™131, from E. I. duPont de Nemours), is further added. The composition isallowed to react for about 4 hours and is ready for application. In thissystem, the alcohol prevents formation of a two-phase mixture.

[0259] In any of the above formulations, the amount of alcohol or otherdiluent can be increased at will, e.g., to reduce the solids loadinglevel, improve sprayability or flowability, or otherwise, if necessary,further increase phase stability.

EXAMPLE 1

[0260] Both new and existing (corroded) air-conditioning units (TheTrane Company, Jacksonville, Fla.), located in a Jacksonville ElectricAuthority sewage treatment plant were treated with a coating compositionaccording to the above Referential Example 1, or were left untreated.The coating compositions were applied, after the units were thoroughlywashed, one to three times, with soapy water, rinsed and dried, usinghand held pump sprayers. The applied coatings, before beginning to gel,may be wiped with a cloth or sponge to remove excess or pooled coatingcomposition.

[0261] In this location, all metal surfaces and parts of the units arenormally reduced to inoperable condition by gases (e.g., flue gases) andcorrosive chemicals after as little as two months operation, and ingeneral, after only 4 to 6 months, on average. Power usage was monitoredby either Florida Power and Light or by Jacksonville Electric Authority.

[0262] Thermal cooling changes were monitored by The Trane Company.Improvements for highly corroded units were as high as 84%. Improvementsfor new units ranged from 1 to 10%. Moreover, the units treatedaccording to this invention were examined by an independent laboratoryand found to have only superficial corrosion after more than 22 months.It is also observed that the coated units stay cleaner longer than theuncoated units and are more easily cleaned.

[0263] Similar results will be obtained using the coating compositionsof other Referential Examples given above.

EXAMPLE 2

[0264] Air conditioning units in the U.S. Naval Facility at NS Mayport,Jacksonville, Fla. were tested with the coating composition as preparedin the above Referential Example 8. In this case, the entire unit,including the external electrical boxes, cabinets, screws, valves,cooling fins, wires. etc., was coated with the invention coatingcomposition. The units are first thoroughly washed with soapy water,rinsed and dried, before the coating is applied. The application can beachieved using any type of manual sprayer, or with a mechanical sprayer.For comparison, units were either coated with conventional organiccoatings, were overcoated on the organically coated units with a coatingcomposition according to this invention, were coated directly on theuntreated unit or were not coated. The units coated with the silanecoating compositions of the present invention were substantiallycorrosion free after more than one years service. In contrast, theorganically treated unit and the untreated unit underwent substantialcorrosion in as little as two months.

[0265] Similar results may be obtained using coating compositions ofother representative compositions of the above Representative Examples.

Example 3

[0266] By applying the coating composition of Referential Example 1B tothe evaporator of an HVAC unit located on the outside of an apartmentbuilding or office building, the coated evaporator is able to preventgrowth or collection of fungal spores and bacteria, thereby preventingfuture transport of the undesirable microorganisms into the buildingthrough the HVAC system. Similar results can be achieved with otherrepresentative coating compositions described in the above ReferentialExamples or elsewhere within the above disclosure.

What is claimed is:
 1. A method for improving efficiency of heattransfer from a heat transfer medium flowing in heat transfer contactwith a heat transfer surface of a thermally conductive component of aheat transfer system across said heat transfer surface, said methodcomprising coating at least a portion of said heat transfer surface witha low viscosity, penetrating, curable, reactive, film-forming, coatingcomposition and curing the composition to thereby form an at leastsubstantially continuous glass-like coating on said heat transfersurface, said coating extending into voids and defects which may bepresent in said heat transfer surface, whereby a thermally conductivecorrosion protective layer is provided on said heat transfer surface. 2.The method of claim 1, wherein said coating composition comprises anaqueous or non-aqueous oligomeric silane coating composition formed byadmixing (a) at least one silane of the formula (1) R¹_(n)Si(OR²)_(4−n)  (1) where R¹ represents a lower alkyl group, a C₆-C₈aryl group or a functional group including at least one of vinyl,acrylic, amino, mercapto, or vinyl chloride functional groups; (b)silane condensation catalyst, and (c) lower alkanol solvent, andoptionally, one or more of (d) colloidal aluminum hydroxide; (e) metalalcoholate of formula (2): M(OR³)_(m)  (2) where M is a metal of valence2, 3 or 4, or mixture of two or more such metals; R represents a loweralkyl group; and, m represents a number or 2, 3 or 4; (f) a silicacomponent selected from the group consisting of alkali metal silicate,ethyl orthosilicate, ethyl polysilicate, and colloidal silica dispersedin lower alkanol; (g) color forming silanol condensation catalyst; (h)epoxysilane; (i) ultrafine titanium dioxide ultraviolet light absorber;(j) water; and (k) co-solvent; and curing the applied coatingcomposition.
 3. The method of claim 2, wherein said oligomeric silanecoating composition comprises (I) an aqueous coating compositioncomprising a dispersion of divalent metal cations in lower aliphaticalcohol-water solution of the partial condensate of at least one silanolof the formula RSi(OH)₃, wherein R is a radical selected from the groupconsisting of lower alkyl, vinyl, phenyl, 3,3,3-trifluoropropyl,gamma-glycidyloxypropyl, and gamma-methacryloxypropyl, at least about 70percent by weight of the silanol being CH₃Si(OH)₃, acid in amount toprovide a pH in the range of from about 2.5 to about 6.2, said divalentmetal cations being present in an amount of from about 1.2 millimoles toabout 2.4 millimoles, per molar equivalent of the partial condensate,calculated as methyl silane sesquioxide.
 4. The method of claim 2,wherein the oligomeric silane coating composition comprises (II) (A) atleast one silane of the formula (I) R¹Si(OR²)₃  (1) wherein R¹ is alower alkyl group, a phenyl group or an N-(2-aminoethyl)-3-aminopropylgroup, and R² is a lower alkyl group; (B) acid component selected fromthe group consisting of water-soluble organic acids, H₃BO₃ and H₃PO₃;and (D) water.
 5. The method of claim 2, wherein the oligomeric silanecoating composition comprises, (III) a non-aqueous coating compositionformed by admixing (A) at least one silane of formula (1) R¹_(n)Si(OR²)_(4−n)  (1) wherein R¹ represents lower alkyl, phenyl,3,3,3-trifluoropropyl, γ-glycidyloxypropyl, γ-(meth)acryloxypropyl,N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group; R³ representslower alkyl group; and n is a number of 1 to 2; and (E) (i)vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide; and/or (iii)at least one metal alcoholate of formula (2) M(OR³)_(m)  (2) wherein Mrepresents a metal of valence m, R³ represents lower alkyl group; and mis a number of 2, 3 or
 4. 6. The method of claim 2, wherein theoligomeric silane coating composition comprises, (IV) a non-aqueouscoating composition formed by admixing (A) at least one silane offormula (1) R¹ _(n)Si(OR²)_(4−n)  (1) wherein R¹ represents lower alkyl,phenyl, 3,3,3-trifluoropropyl, γ-glycidyloxypropyl,γ-(meth)acryloxypropyl, N-(2-aminoethyl)-3-aminopropyl, or aminopropylgroup; R² represents lower alkyl or acetyl group; and n is a number of 1to 2; (B) boric acid, optionally dissolved in lower alkanol; (E) (i)vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide; and/or (iii)at least one metal alcoholate of formula (2) M(OR³)_(m)  (2) wherein Mrepresents a metal of valence m, R³ represents lower alkyl group m is annumber of 2, 3 or 4; and. (F) silica component selected from the groupconsisting of ethyl ortho-silicate, ethyl polysilicate and colloidalsilica, dispersed in lower alkanol.
 7. The method of claim 2, whereinthe oligomeric silane coating composition comprises, (V) a non-aqueouscoating composition formed by admixing (A) at least one silane offormula (1) R¹ _(n)Si(OR²)_(4−n)  (1) wherein R¹ represents lower alkyl,phenyl, 3,3,3-trifluoropropyl, γ-(meth)acryloxypropyl,N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group; R² representslower alkyl or acetyl group; and n is a number of 1 to 2; (A′)γ-glycidyloxypropyloxytrimethoxysilane; (B) boric acid, optionallydissolved in lower alkanol; (E) (i) vinyltriacetoxysilane, (ii)colloidal aluminum hydroxide; and/or (iii) at least one metal alcoholateof formula (2) M(OR³)_(m)  (2) wherein M represents a metal of valencem, R³ represents lower alkyl group m is an number of 2, 3 or
 4. 8. Themethod of claim 2, wherein the oligomeric silane coating compositioncomprises (VI) an oligomeric silane coating composition formed byadmixing (A) at least one silane of formula (1) R¹_(n)Si(OR²)_(4−n)  (1) wherein R¹ represents lower alkyl, phenyl, or afunctional group containing at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional group; and R² is a lower alkylgroup; (B) acid component comprising a member selected from the groupconsisting of water-soluble organic acids, H₃BO₃ and H₃PO₃; and (D)water.
 9. The method of claim 2, wherein the oligomeric silane coatingcomposition comprises, (VII) an aqueous oligomeric silane coatingcomposition formed by admixing (A) at least one silane of formula (1) R¹_(n)Si(OR²)_(4−n)  (1) wherein R¹ represents lower alkyl, phenyl, or afunctional group containing at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional group; and R² is a lower alkylgroup; (C) alkali component; and (D) water.
 10. The method of claim 2,wherein the oligomeric silane coating composition comprises (VIII) anaqueous coating composition formed by admixing (A) at least one silaneof the formula (1) R¹Si(OR²)₃  (1) wherein R¹ is a lower alkyl group, aphenyl group or a bifunctional silane containing vinyl, acrylic, amino,or vinyl chloride functional group; and R² is a lower alkyl group; (E)(ii) colloidal aluminum hydroxide, (iii) metal alcoholate of the formula(2) M(OR³)_(m)  (2) wherein M is a metal of valence m, R³ is a loweralkyl group, m is an integer of 3 or 4, or mixture of (ii) and (iii);and (D) water.
 11. The method of claim 2, wherein the oligomeric silanecoating composition comprises (IX) an aqueous coating composition formedby admixing (A) at least one silane of the formula (1) R¹Si(OR²)₃  (1)wherein R¹ is a lower alkyl group, a phenyl group or a bifunctionalsilane containing vinyl, acrylic, amino, or vinyl chloride functionalgroup; and R² is a lower alkyl group; (D) water; (H) lower alkanol; and(G) chromium acetate hydroxide.
 12. The method of claim 2, wherein theoligomeric silane coating composition comprises (X) an aqueous coatingcomposition formed by admixing (A) at least one silane of the formula(1) R¹Si(OR²)₃  (1) wherein R¹ is a lower alkyl group, a phenyl group ora functional group including at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional group; and R² is a lower alkylgroup; (D) water; (F) alkali metal silicate, which may be hydrolyzed;(H) lower alkanol; and (E) (ii) colloidal aluminum hydroxide, (iii)metal alcoholate of the formula (2) M(OR³)_(m)  (2) wherein M is a metalof valence m, R³ is a lower alkyl group, m is an integer of 3 or 4, ormixture of (ii) and (iii).
 13. The method of claim 2, wherein theoligomeric silane coating composition comprises, (XI) a non-metallicaqueous coating composition formed by admixing (A) at least one silaneof the formula (1) R¹Si(OR²)₃  (1) wherein R¹ is a lower alkyl group, aphenyl group or a functional group including at least one of vinyl,acrylic, amino, mercapto, or vinyl chloride functional group; and R² isa lower alkyl group; (A″) 3-(2-aminoethylamino)propyltrimethoxysilane or3-aminopropyltrimethoxysilane; (D) water; (I) epoxide silane; and (H)lower alkanol.
 14. The method of claim 2, wherein the oligomeric silanecoating composition comprises, (XII) an aqueous coating compositionformed by admixing (A) at least one silane of the formula (1)R¹Si(OR²)₃  (1) wherein R¹ is a lower alkyl group, a phenyl group or afunctional group including at least one of vinyl, acrylic, amino,mercapto, or vinyl chloride functional group; and R² is a lower alkylgroup; (B) boric acid; (C) at least one alkali component comprising anhydroxide or carbonate of divalent metal; (D) water; (J) ethylpolysiloxane; and (H) lower alkanol.
 15. The method according to claim1, for increasing the contact area between first and second heattransfer surfaces in thermal contact with each other, thereby improvingthe heat transfer efficiency across the thermally contacting heattransfer surfaces, said method comprising, applying said low viscosity,penetrating coating composition to the thermally contacting heattransfer surface of at least one of said first and second heat transfersurfaces.
 16. The method according to claim 15, wherein the coatingcomposition comprises an aqueous or non-aqueous oligomeric silanecoating composition formed by admixing (a) at least one silane of theformula (1) R¹ _(n)Si(OR²)_(4−n ()1) where R¹ represents a lower alkylgroup, a C₆-C₈ aryl group or a functional group including at least oneof vinyl, acrylic, amino, mercapto, or vinyl chloride functional groups;(b) silane condensation catalyst, and (c) lower alkanol solvent, andoptionally, one or more of (d) colloidal aluminum hydroxide; (e) metalalcoholate of formula (2): M(OR³)_(m)  (2) where M is a metal of valence2, 3 or 4, or mixture of two or more such metals; R represents a loweralkyl group; and, m represents a number or 2, 3 or 4; (f) silicacomponent selected from the group consisting of alkali metal silicate,ethyl orthosilicate, ethyl polysilicate, and colloidal silica dispersedin lower alkanol; (g) color forming silanol condensation catalyst; (h)epoxysilane; (i) ultrafine titanium dioxide ultraviolet light absorber;(j)water; (k) co-solvent; and wherein the oligomeric coating compositionis allowed to cure to a film thickness of from about 5 to about 150millions of an inch, thereby filling any microvacancies in said heattransfer surfaces.
 17. The method according to claim 1, for improvingthe efficiency of heat exchange apparatus of the type wherein a metalheat transfer surface is swaged or force fit to a metal heat transferfluid conveyance, said method comprising, applying to the interfacebetween the heat transfer surface and the conveyance said low viscosity,penetrating coating composition whereby the coating composition willdisplace gasses and liquids in said interface; and allowing the coatingcomposition to cure to a film thickness of from about 5 to about 150millions of an inch, and fill any microvacancies in said metal surfacesat said interface.
 18. The method according to claim 17, wherein saidcoating composition comprises an aqueous or non-aqueous oligomericsilane coating composition formed by admixing (a) at least one silane ofthe formula (1) R¹ _(n)Si(OR²)_(4−n)  (1) where R¹ represents a loweralkyl group, a phenyl group or a functional group including at least oneof vinyl, acrylic, amino, mercapto, or vinyl chloride functional groups;(b) silane condensation catalyst, and (c) lower alkanol solvent, andoptionally, one or more of (d) colloidal aluminum hydroxide; (e) metalalcoholate of formula (2): M(OR³)_(m)  (2) where M is a metal of valence2, 3 or 4, or mixture of two or more such metals; R represents a loweralkyl group; and, m represents a number or 2, 3 or 4; (f) a silicacomponent selected from the group consisting of alkali metal silicate,ethyl orthosilicate, ethyl polysilicate, and colloidal silica dispersedin lower alkanol; (g) color forming silanol condensation catalyst; (h)epoxysilane; (i) ultrafine titanium dioxide ultraviolet light absorber;(j) water; (k) cosolvent.
 19. The method according to claim 1, whereinsaid heat transfer surface comprises a fin and tube heat transferdevice.
 20. A heat transfer system comprising a metal heat transfersurface, wherein said metal heat transfer surface is coated with a curedlow viscosity, penetrating, curable, reactive, film-forming, coatingcomposition whereby the cured coating composition has a film thicknessof from about 5 to about 150 millions of an inch, and fills anymicrovacancies in said metal surfaces.
 21. The heat transfer systemaccording to claim 20, wherein the heat transfer surface of said heattransfer system comprises a fin and tube heat exchange device.
 22. Theheat transfer system according to claim 20, wherein the heat transfersurface comprises an evaporator, said coating being resistant toadhesion of microorganisms.